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How to choose power amplifier for background music project

When designing background music, we often entangled whether to use constant voltage power amplifier equipment or constant resistance power amplifier equipment, so today we will talk about the difference between these two power amplifiers in the background music project, and give us when doing engineering design. Make a reference.

The difference between constant voltage power amplifier and constant resistance power amplifier

First, let me explain the difference between constant voltage power amplifier and constant resistance power amplifier. The constant voltage power amplifier actually adds a set of transformer output on the basis of the constant resistance power amplifier, which is not different from the constant resistance power amplifier in function. So what is the role of adding this transformer?

Because when designing a public broadcasting project, the engineer will need to design and install a lot of audio equipment, and the number is not necessarily, so it will create a situation where the output impedance of the successful amplifier does not match the total input impedance of the audio, usually the constant resistance function can The output impedance tolerated is in the range of 4-16Ω, and the impedance of the usual audio equipment is about 8Ω. If multiple audio output devices are to be connected at a time, the total impedance of the audio equipment must be greater than 16Ω or less than 4Ω, or the sound engineer The input impedance of the final audio equipment can be controlled between 4 and 16 Ω through precise calculations, but the impedance of the cable has not been calculated yet. If the impedance of the cable is added, the calculation will be very complicated.

In order to solve the problem of impedance matching, engineers thought of using a transformer for impedance isolation. With the audio output transformer, the amplifier and the audio equipment are isolated from each other. The input impedance of the audio only needs to match the impedance base of the transformer. , And the impedance of the transformer can withstand a larger range, so the engineer is more free when designing how many audio equipment is needed, eliminating the need for complicated impedance calculations, and simply matching the power. .

At the same time, with the audio output transformer, the voltage of the audio signal can be increased. Friends who know the principle of high-voltage transmission should know the benefits of increased voltage transmission, that is, it can reduce the loss on the transmission line, so after using the audio transformer isolation Another advantage brought is that the loss on the wire is reduced.

Why is the sound quality of the constant voltage power amplifier not as good as the constant resistance power amplifier?

Although the use of an audio isolator (transformer) solves the problem of impedance matching between the power amplifier and the audio, the transformer also has a filtering effect in the circuit, because the transformer itself is an inductor, so high-frequency electrical signals will be filtered. In this way, some high-frequency signals in the sound will be lost after being filtered by the transformer, but this part of the missing high-frequency signals cannot be fully perceived by ordinary people, although the maximum sound frequency we can hear It is 20KHz, but after research and testing, it is difficult for ordinary people to perceive the frequency of sound above 15KHz. This is actually a technique used in audio compression algorithms. It is reduced by removing the frequency that is difficult to perceive by the human ear. The size of audio files, MP3 is the most successful example. The frequency of the transformer filtering is basically greater than 15KHz, so the frequency loss in the high-pitched part is still relatively small, but there will be a little high-pitched distortion compared with the constant resistance equipment.

The second is the bass part of the sound, because the bass frequency is relatively low, the transformer will not filter this part of the low-frequency electrical signal. However, the audio transformer induces a current through the changing magnetic field to output to the audio equipment, so the magnetic field changes generated by the low-frequency signal may not be enough to drive and generate enough output current, and this part of the low-frequency signal is also lost.

Through the above analysis, we can know why the sound quality of the constant voltage power amplifier is less than that of the constant resistance power amplifier. It is precisely because the output transformer is used that part of the treble and bass signals will be lost. However, these lost audio signals are for ordinary people. The hearing effect is not great, unless it is a professional, it is usually not possible to hear the missing details.

Then how to choose a power amplifier when designing sound system engineering

Based on the above analysis, such a selection criterion can basically be drawn. First of all, for the occasions with high sound quality requirements, only a constant resistance power amplifier can be used, because the constant resistance power amplifier is 100% reduction of the sound, and the sound quality is better.

And if it is in an open environment, such as a garden, a playground or a square, then it is a better choice to use constant pressure equipment, because in an open occasion, the air itself is also a kind of filtering element, which will naturally affect high-frequency signals. Play a filtering role, so even if the best constant resistance equipment is used, frequency filtering will occur naturally, so the use of constant pressure equipment is a balanced choice in terms of the final effect and design complexity.

In indoor public places, the choice should be made according to the height of the floor and the enclosed environment. The situation with a floor higher than 3 meters can basically be handled as an open place.

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